Messages in this thread | | | Subject | Re: [PATCH] proc: pagemap: Hold mmap_sem during page walk | From | Matt Mackall <> | Date | Wed, 31 Mar 2010 22:20:23 -0500 |
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On Wed, 2010-03-31 at 18:33 -0700, Linus Torvalds wrote: > > On Wed, 31 Mar 2010, Matt Mackall wrote: > > > > Linus, I must say your charm has really worn thin. I've just stuck a > > post-it on my monitor saying "don't be Linus" to remind me not to be > > rude to my contributors. > > You didn't actually answer the problem, though. > > I'm rude, because I think the code is buggy.
And what does that achieve? I've got plenty of other work I could be doing where people are nice to me when asking me to fix bugs.
> I pointed out how, and why I > think it's pretty fundamental. You quoted it, but you didn't answer it.
Yes, I was muddling the distinction between pinned in page cache and pinned in the mm, and you've just now re-clarified it for me. So I'll agree the current code is bogus.
> So Matt, please actually address the _bug_ I pointed out rather than talk > about other things. And yes, getting rid of the vma accesses sounds like > it would fix it best. If that means that it doesn't work for hugepages, so > be it.
That'd actually take us back to where it was when it hit mainline, which would make a lot of people unhappy. I wouldn't be one of them as there thankfully aren't any huge pages in my world. But I'm convinced put_user() must go. In which case, get_user_pages() stays, and I've got to switch things to direct physical page access into that array.
Even if I fix that, I believe San's original bug can still be triggered though, as all the new callers to find_vma are run outside of the target's mm_sem. Fixing that should be reasonably straight-forward.
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